Modeling of a Back-Illuminated HgCdTe MWIR Avalanche Photodiode with Alloy Gradients

We present results from 2D Monte Carlo simulations of a mid-wave infrared (MWIR) back-illuminated planar n-on-p HgCdTe electron-initiated avalanche photodiode (e-APD). The main objective of this work has been to study the dependence of the multiplication gain, excess noise factor, and response time on the position where the incident photon is absorbed. We also quantify the effects of the naturally occurring vertical alloy gradient electric fields in APDs grown by liquid phase epitaxy. The simulated gain is relatively independent of the excitation position, but a small increase is observed near the edges of the APD. The excess noise factor is around 1.2 for all positions. It is found that the alloy gradient field helps to speed up the response of the device, especially for excitation positions far away from the multiplication region.